In the manufacture of a semiconductor device such as a large scale integrated circuit (LSI) and a very large scale integrated circuit (VLSI), or a liquid crystal display panel, a semiconductor wafer or a mother substrate for a liquid crystal display panel is irradiated with exposure light, whereby a pattern is transferred onto the surface of the wafer or the mother substrate; however, if a dust particle exists on the stencil, this particle can absorb or bend the light to thereby deform the pattern or blur the edges of the pattern transferred; furthermore the underlying surface is also blackened by soiling, whereby the size, quality, appearance and the like of the semiconductor wafer or the liquid crystal display panel mother substrate are degraded. In the present invention, an “exposure stencil” shall mean a mask for lithography or a reticle.
In order to prevent these problems, the operation of exposing the substrates is generally conducted in a clean room. However, even in a clean room environment, it is not always easy to keep the exposure stencil dust-free, and hence in order to fend off the dust from the surface of the exposure stencil, a pellicle which passes exposure light well is attached to cover the exposure stencil. In this manner, the dust is prevented from reaching the surface of the exposure stencil but can only alight on the pellicle membrane so that, if the exposure light is set to focus on the pattern of the exposure stencil, the dust on the pellicle membrane fails to shadow itself in the transferred pattern.
In general, a pellicle is manufactured by adhering a pellicle membrane to one annular face of a pellicle frame. The pellicle membrane is made of a nitrocellulose, cellulose acetate, a fluorine-containing polymer, or the like that has a high transmittance with respect to an exposure light (such as g-line, i-line, KrF excimer laser, ArF excimer laser, and F2 excimer laser). The pellicle frame is made of an aluminum alloy such as A7075, A6061, and A5052, which are black almite-anodized in the surface, or of a stainless steel or of polyethylene, etc.
The adhesion of the pellicle membrane to an annular face of the pellicle frame is effected by laying a solvent capable of dissolving the pellicle membrane on the annular face and placing the membrane over the solvent and drying the latter by air flow, or by using an adhesive such as acrylic resin, epoxy resin and fluorine-containing resin. Furthermore, on the other one of the two annular faces of the frame is laid a stencil-bonding agglutinant layer made of a polybutene resin, a polyvinyl acetate resin, an acrylic resin, a silicone resin or the like for attaching the pellicle frame to the exposure stencil, and over this stencil-bonding agglutinant layer is laid a releasable liner for protecting the stencil-bonding agglutinant layer.
A pellicle is set in a manner such that the pellicle frame entirely surrounds the pattern region formed in the surface of the exposure stencil; as the pellicle is installed for the purpose of preventing the dust from adhering to the exposure stencil, the pattern region is isolated from the external atmosphere by means of the pellicle so that the dust outside the pellicle cannot reach the pattern region.
In recent years, the design rules for LSI have been modified in the direction of heightening the resolution density as high as sub-quarter micron order, and this goes hand-in-hand with shortening of the exposure light wavelength. In other words, the formerly prevalent g-line (436 nm) and i-line (365 nm) created by mercury lamps are being replaced by KrF excimer laser (248 nm), ArF excimer laser (193 nm), F2 laser (157 nm) and the like. As the result of increasing exposure resolution, the flatness of the pattern-bearing face of the exposure stencil is very critically inspected after the pellicle is agglutinated to the exposure stencil, so that there is a need for minimizing the pellicle induced deformation of the mask which occurs as the pellicle is agglutinated to the mask.
In particular, the mask deformation caused upon agglutination of the pellicle to the mask is significantly affected by the flatness of the pellicle frame and the quality (softness) and the dimension of the stencil-bonding agglutinant layer. Accordingly there have been made efforts for suppressing the mask deformation, such as a pellicle in which the agglutinant layer is shaped to have a higher flatness, a pellicle where the flatness of the frame is controlled and a pellicle where a softer agglutinant is employed so as to minimize the mask deformation at the time of pellicle bonding.
For example, IP Publication 1 teaches about a pellicle whose agglutinant layer has a facial flatness of 15 micrometers or smaller. However, despite the efforts narrated above, it has been yet an unsolved problem to completely suppress the pellicle induced deformation of the mask.